Towards new molecular superconductors: a first study of alkali metal reduced aromatic cryptands as `pseudo-fulleridesʹ

The search for new molecular superconductors based upon concepts derived from the interpretation of alkali fullerides superconductivity led to the study of an aromatic cryptand (IHIC) considered as `pseudo-fullereneʹ. New solids made of IHIC mono or di-reduced by potassium, rubidium and cesium were investigated. Low field microwave absorption (LFMA) signals appeared at 20 K for IHIC–Rb and IHIC–K (1:1), although these observations could not be confirmed by AC susceptibility or SQUID magnetometry. IR spectroscopy was used to probe the integrity of the final solid. EPR spectra consisted of a single symmetric line, combination of a Gaussian and of a Lorentzian lineshape, down to 4.2 K. However, the paramagnetic contribution of the reduced molecular species was too high to allow the observation of any transition at low temperature. Although two samples had a semiconductor like conductivity behavior as a function of temperature at high temperature, no indication of the presence of conduction electrons could be observed on the EPR spectrum. The LFMA measurements obtained can be considered as hints of superconductivity, thus opening the route towards new materials.